Tissue distribution of the rat analogue of decay-accelerating factor

In humans, decay-accelerating factor (DAF) is a widely distributed, cell-bo und inhibitor of the complement activation enzymes and plays a key role in regulating complement activation, preventing the generation of anaphylotoxi ns and opsonins, and protecting against complement-mediated lysis. Rodent a nalogues of DAF have recently been identified, providing a new avenue for t he analysis of function. Rat DAF was cloned in our laboratory. Here we desc ribe the generation of monoclonal antibodies (mAbs) against rat DAF, using transfected cells as immunogen, and their use in the analysis of the distri bution of DAF in the rat by flow cytometry, Western blot analysis and immun ohistochemistry. One of the mAbs was found to block the complement inhibito ry function of rat DAF, offering the prospect of neutralization of DAF func tion in vivo. The antibodies have also been used for purification of DAF fr om rat erythrocytes by affinity chromatography. Rat DAF purified in this ma nner was similar in molecular mass to human DAF. The purified protein incor porated into lipid membranes, confirming the presence of a glycolipid ancho r, and incorporated protein strongly inhibited the rat C3 convertase. Rat D AF was strongly expressed an endothelia throughout the animal and was also present in most tissues and organs. DAF expression was weak or absent in th e brain and on circulating and spleen-resident T cells. Strong DAF expressi on observed in the kidney was restricted to the glomerulus and Bowman's cap sule. DAF expression in the testis was found only in association with the l ater stages of spermatogenesis.